[llvm] [ADT] Remove StringRef::equals (PR #98735)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-solaris11-sparcv9` running on `solaris11-sparcv9` while building `llvm` at step 4 "build stage 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/13/builds/712

Here is the relevant piece of the build log for the reference:
```
Step 4 (build stage 1) failure: 'ninja -j8' (failure)
...
[103/4068] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/WithColor.cpp.o
[104/4068] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/Z3Solver.cpp.o
[105/4068] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/xxhash.cpp.o
[106/4068] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/raw_ostream.cpp.o
[107/4068] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/YAMLTraits.cpp.o
[108/4068] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/DynamicLibrary.cpp.o
[109/4068] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/raw_socket_stream.cpp.o
[110/4068] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/YAMLParser.cpp.o
[111/4068] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/RWMutex.cpp.o
[112/4068] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/Path.cpp.o
FAILED: lib/Support/CMakeFiles/LLVMSupport.dir/Path.cpp.o 
/opt/llvm/17/bin/clang++ -DGTEST_HAS_RTTI=0 -D_DEBUG -D_FILE_OFFSET_BITS=64 -D_GLIBCXX_ASSERTIONS -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/stage1/lib/Support -I/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/llvm/lib/Support -I/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/stage1/include -I/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/llvm/include -I/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/llvm/include/llvm/Support/Solaris -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -Werror=global-constructors  -O -DNDEBUG -UNDEBUG -std=c++17  -fno-exceptions -funwind-tables -fno-rtti -MD -MT lib/Support/CMakeFiles/LLVMSupport.dir/Path.cpp.o -MF lib/Support/CMakeFiles/LLVMSupport.dir/Path.cpp.o.d -o lib/Support/CMakeFiles/LLVMSupport.dir/Path.cpp.o -c /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/llvm/lib/Support/Path.cpp
In file included from /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/llvm/lib/Support/Path.cpp:1200:
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/llvm/lib/Support/Unix/Path.inc:519:18: error: no member named 'equals' in 'llvm::StringRef'
  519 |   return !fstype.equals("nfs");
      |           ~~~~~~ ^
1 error generated.
[113/4068] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/Memory.cpp.o
[114/4068] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/Process.cpp.o
[115/4068] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/Threading.cpp.o
[116/4068] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/Program.cpp.o
[117/4068] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/Signals.cpp.o
[118/4068] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/VirtualFileSystem.cpp.o
[119/4068] Building CXX object lib/TableGen/CMakeFiles/LLVMTableGen.dir/DetailedRecordsBackend.cpp.o
ninja: build stopped: subcommand failed.

```

https://github.com/llvm/llvm-project/pull/98735